Tunes only used in commercials (7)
I believe the answer is:
adjusts
'tunes' is the definition.
The definition and answer can be both related to change as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?
'only used in commercials' is the wordplay.
'only' becomes 'just' (synonyms).
'used in' means one lot of letters goes inside another.
'commercials' becomes 'ads' (advertisements).
'just' inserted into 'ads' is 'ADJUSTS'.
Can you help me to learn more?
(Other definitions for adjusts that I've seen before include "suits" , "Alters to regulate" .)